ST. LOUIS — Do not expect to find the Mona Lisa here. Or a Tyrannosaurus rex skeleton.

Instead, this museum features a 10-story slide that whizzes guests of all ages from the roof to a subterranean cave.

Welcome to City Museum, an ever-evolving art project that is unlike any museum you have ever seen. In fact, calling it a museum is a bit of a stretch. The converted shoe warehouse is closer to a mad scientist's workshop than a cultural institution.

That does not mean it isn't fun.

There is an oversized ball pit, a miniature railroad, rooftop Ferris wheel and countless hands-on exhibits. Throw in a 1924 Wurlitzer pipe organ, neon signs, preserved butterflies and the world's largest pencil and you have one of the world's most eclectic collections.

The museum, which saw 710,000 visitors last year, is a lasting tribute to the imagination of its late founder, Bob Cassilly, an artist who bought the shoe warehouse in 1993. In, 1995, Cassilly started construction and two years later City Museum opened.

Revived downtownHis vision for City Museum is credited by many with helping to bring people back to the downtown neighborhood where the museum is sited. Once filled with vacant industrial buildings, the area is now dotted with trendy restaurants, clubs and apartments. The museum's warehouse also houses artists' studios, luxury lofts, a catering business and a company that sells fake flowers and Christmas trees. Cassilly died in an accident in September while working on a new project, converting an old cement plant into an amusement park just outside St. Louis.

There never was a plan for how to assemble City Museum. Parts just came together. A school bus was placed on the roof. An old airplane was acquired. A large collection of bee hives, bugs and stuffed birds made it into the museum after a building maintenance worker let it be known he had been collecting them since he was 13.

Today, the eclectic mix of art and artifacts continues to grow with a statue from a Bob's Big Boy restaurant, a sign — never quite explained — announcing "the dark side of the corn dog" and a skateless skateboard park where visitors can play (but not skate) on the ramps and half-pipes. Rag-doll making classes are offered near a woman who advertises her services as "Storyteller and snowflake lady. NOT a Fortuneteller!"

An arts and crafts area and floor-to-ceiling chalkboard ensure that this is a hands-on experience for all.

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"If you're staring at a statue, there's a feeling there. But once you climb on that statue, and you become a part of that statue, it's a whole different feeling," Erwin says.

Kids keep busyDuring the day, children run through the halls, fly down slides, crawl on catwalks, press their faces against the glass of an onsite aquarium and snake their way through caves.

One boy recently shouted toward his dad with gleeful enthusiasm: "I'm going to go explore that tunnel. If it leads somewhere cool, I'll come back and get you." A few moments later, he came back saying: "It goes pretty far, let's go explore!"

At night the museum takes on a new life. On weekends, lights are turned off, flashlights are handed out and guests are left to explore until 1 a.m. in near darkness. If that is too spooky, visitors can head up to the roof and sip $7 mojitos.

There really is no theme nor any type of order to the museum. The philosophy, Erwin explains, is more "organized chaos, play it by ear and see what happens."

For example, the museum was offered a donation of lawn mower tires. "We didn't want those tires, but we wanted to keep them out of the landfill," Erwin says.

So, the tires were used to build a new wall.

That's fitting for a museum with no dead ends. Every hallway loops around to something else in an effort not to kill the curiosity and momentum of guests.

"People get mad at us all the time for not having a map," Erwin says. "We just want you to explore."

If you go
City Museum: 701 N. 15th St., St. Louis; 314-231-2489. Admission, $12. Children 2 and under, free. Roof access is an additional $5; the aquarium an extra $6.

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